In humans and in animals, normal aging is often associated with a marked deterioration in both the quantity and the quality of motor activity. In addition to postural and locomotor deficits, alterations in orolingual and pharyngeal motor function are also associated with human aging. Like locomotor deficits, these disturbances have been found to contribute to an increased risk of death in the elderly. The fact that orolingual motor deficits are also prevalent in Parkinson's disease suggests that alterations in the basal ganglia may play a role in their expression. Although there is considerable evidence linking the basal ganglia to locomotor function, a role for these nuclei in orolingual motor function remains to be examined in animal models of normal aging. The purpose of this grant is to measure orolingual motor function in young, middle-aged and aged animals and to determine relationships between age, behavioral performance and measures of nigrostriatal dopamine (DA) function. In these studies, thirsty rats will be trained to lick water from an isometric force-sensing disc while biophysical and temporal characteristics of tongue movements are measured. A sensorimotor challenge will require rats to extend their tongues increasing distances in order to contact the force-sensing disc. Nigrostriatal DA function will be measured in freely moving animals using intracerebral microdialysis. The effects of antiparkinson drugs will be compared to glial cell line-derived neurotrophic factor (GDNF). These studies should yield novel and valuable information regarding relationships between aging, orolingual motor function and nigrostriatal DA integrity.